For applications such as the production of radioisotopes or neutrons, it is common practice to bombard a comparatively thick target with a beam of charged particles from a particle accelerator in order to cause desired nuclear reactions in said target. Here, the particle accelerator can be e.g. a radiofrequency linear accelerator. By way of example, the charged particles can be protons.
The generation of the accelerated particle beam is connected with a significant energy input. In the case where a thick target is used, the energy transferred to the charged particles as kinetic energy by the particle accelerator largely remains in the target after the particles impact on said target. Some of the energy is emitted as bothersome x-ray bremsstrahlung. The energy remaining in the target leads to heating of the target, which makes cooling of the target necessary. The maximum possible cooling power restricts the maximum employable flux of particles shot at the target.
The portion of the energy used for desired nuclear reactions is small when a thick target is used since the desired nuclear reactions are generally only possible in a tightly delimited energy interval of the energy of the impacting particles.